Segment a-a of helical gear 3 is the rocker arm of four-bar linkage ABCD. When crank 1 rotates about fixed axis A, link 3 either rotates or reciprocates link 4 on which worm b-b is mounted. Rotation of link 4 is obtained by proper selection of the pitch and helix angle of the worm.
$1739$GL,5L$